[DAG] Legalize abs(x) -> umin(x,sub(0,x)) iff umin/sub are legal

If umin() is legal, this is likely to result in smaller codegen expansion for abs(x) than the xor(add,ashr) method.

Followup to D92095

Alive2: https://alive2.llvm.org/ce/z/8nuX6s  https://alive2.llvm.org/ce/z/q2hB9w